It is general practice in the field of electrostatic copying apparatus to set effective lives for the photosensitive body and developing device in order to ensure production of good copies. Further, in order to facilitate maintenance, a system has been recently adopted for copying machines in which the photosensitive body and the developing device are replaceable processing units. When the units have reached the end of their respective lives, an expert serviceman can replace them.
In a conventional copying apparatus, the frequency of regular service calls is based on how frequently the apparatus is utilized by an averager user. Therefore, users who make more frequent use of a copying apparatus than average users have no choice but to carry out maintenance themselves since their business operations would be slowed if they waited for a regular call by an expert serviceman. Since the general user has little related technical knowledge or experience, in most cases this maintenance is difficult to carry out.
Similarly, the general procedure for deciding when to replace a photosensitive body is to periodically check a total counter on the apparatus main body and replace the photosensitive body when the number of copies has reached a predetermined value corresponding to the photosensitive body's effective life. However, since the photosensitive body replacement period is much longer than that of the developing service, individuals in a busy office are liable to forget to check this properly. Further, the deterioration of images is not easily noticed, since it progresses only a little each day. As a result, there is a tendency to continue using the photosensitive body well beyond its effective life. Because of this, there is a strong demand for measures to make user maintenance of this type of equipment easier.
Recently, a twin color copying apparatus which can copy selectively with a black color toner and a red color toner has been developed. Either the black developing device containing carrier particles and black color toner or the red developing device containing carrier particles and red color toner is selectively set into the apparatus main body corresponding to the desired color copy. Therefore, it is difficult to accurately count the number of image formations for each color developing device by reference to the counter provided on the apparatus main body. As a result, the effective life of the above carrier particles in each color developing device may come to an end unexpectedly so that the user will not have sufficient time to prepare a new developing device. In such cases, the main apparatus must remain unused until the new device is readied.